It is known that there are various methods of transmitting serial signals in serial communications. FIG. 17 through FIG. 20 illustrate typical ones of such methods.
FIG. 17 exemplifies a method of the related art for transmitting serial signals in serial communications.
In FIG. 17, a data signal SdA is a common data signal, in which data values are directly represented by signal levels, and data values are extracted from the data signal SdA by using a synchronization signal SaA, which delimits different data. In this method, two signals, such as the data signal SdA and the synchronization signal SaA are used.
FIG. 18 exemplifies another method of the related art for transmitting serial signals in serial communications.
In FIG. 18, a data signal SdB is a pulse width modulation signal, in which signal intervals are constant, and pulse widths differ between when the data value is “0” and when the data value is “1”. With this method, although the code interval thereof is a problem, it is possible to perform asynchronous operations.
For this technique, for example, reference can be made to U.S. Pat. No. 698,066, U.S. Pat. No. 5,862,354, U.S. Pat. No. 5,978,927, U.S. Pat. No. 6,108,751, U.S. Pat. No. 6,239,732, U.S. Pat. No. 6,412,072, and U.S. Pat. No. 5,803,518.
FIG. 19 exemplifies another method of the related art for transmitting serial signals in serial communications.
In FIG. 19, a data signal SdC is a pulse position modulation signal in which pulse positions change along time, and data are sampled with a synchronization signal SaC serving as a time reference.
FIG. 20 exemplifies still another method of the related art for transmitting serial signals in serial communications.
In FIG. 20, a data signal SdD is a signal used in an infrared remote controller, and is obtained by combining the pulse width modulation and the pulse position modulation signal. However, because data intervals are not constant in the data signal SdD, the data signal SdD is an asynchronous signal, therefore, a synchronization signal is not needed.
FIG. 21 is a block diagram illustrating a serial communication device of the related art for performing half-duplex communications.
In FIG. 21, a serial communication device 200 includes a master transmission/reception circuit 201 and a slave transmission/reception circuit 205. The master transmission/reception circuit 201 includes a master transmission circuit 202, a master reception circuit 203, and a master switching section 204 for transmission authority control. Similarly, the slave transmission/reception circuit 205 includes a slave transmission circuit 206, a slave reception circuit 207, and a slave switching section 208 for transmission authority control. Basically, the master transmission circuit 202 is the same as the slave transmission circuit 206, and the master reception circuit 203 is the same as the slave reception circuit 207.
Here, when the transmission authority is on the master transmission/reception circuit 201, data are transmitted from the master transmission circuit 202 of the master transmission/reception circuit 201 to the slave reception circuit 207 of the slave transmission/reception circuit 205. Meanwhile, if the transmission authority is transferred to the slave transmission/reception circuit 205, data are transmitted from the slave transmission circuit 206 of the slave transmission/reception circuit 205 to the master reception circuit 203 of the master transmission/reception circuit 201.
However, as described above, in the related art, a synchronous signal is required. Even if the synchronous signal is not used, the circuits for generating data signals from data or extracting the data from the data signals are complicated. Further, in order to perform the half-duplex communication, the same circuit as that on the master side is required on the slave side, and switching units for switching between transmission operations and reception operations are needed. For this reason, the scale of the circuit is large, and space and cost of the circuit increase.